Posted by David Sherman on Thursday, April 05, 2001 at 11:52PM :
Here's a puzzle: Anybody have an idea about what would cause carbon to build up on the intake side of the intake valves (around the stem and the "upstream" side of the valve)? I'm overhauling a little flathead 4 which had chewed up one of the rod journals and found lots of carbon in the combustion chamber and on the stem sides of both intake and exhaust valves. It's been years since I ran it, but as I recall it ran badly, smoked a bit and did not put out anywhere near full power. At the time, I checked the compression and it was excellent. All cylinders were equally sooted up, and I'd only run it for a few hours since I'd previously had the head off and cleaned it. My best guess is somehow the timing was way off. First I was thinking a stuck valve that only stuck at higher speeds (so the compression test wouldn't catch it) but I wouldn't think all 4 intake valves would stick.
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